Internal combustion engines convert chemical energy associated with a mixture of air and fuel into mechanical power by combustion of the mixture of air and fuel. In particular, many internal combustion engines burn carbon-based fuels, such as, for example, gasoline, diesel fuel, alcohol such as methane and ethane, and/or combinations thereof, such as, for example, a gasoline-alcohol combination sometimes referred to as “E85” (i.e., a mixture of about 85% ethanol and about 15% gasoline). The combustion of carbon-based fuels converts the chemical energy associated with the carbon-based fuel into mechanical power by releasing heat generated during combustion, which, in turn, creates pressure that drives a mechanism, such as, for example, the piston of a reciprocating engine or the rotor of a rotary engine.
Along with releasing heat, combustion of the mixture of air and fuel results in the emission of by-products of the combustion process. For example, combustion may result in the emission of unburned fuel, hydrocarbons such as methane (CH4), oxides of carbon (COx) such as carbon monoxide (CO) and carbon dioxide (CO2), oxides of nitrogen (NOX), water vapor, ozone (O3), and/or other compounds. Of particular concern is the emission of “greenhouse gases,” such as, for example, carbon dioxide (CO2), methane (CH4), ozone (O3), and water vapor.
Renewed interest in the conservation of natural resources and the environment has led to an increased desire to improve the fuel efficiency and reduce the emissions of internal combustion engines. One way to increase the efficiency of internal combustion engines is to harness the maximum amount of energy associated with a unit volume of fuel during combustion by controlling the combustion process such that a greater proportion of the fuel is burned during combustion. This greater efficiency, in turn, effectively reduces the amount of exhaust emissions created during combustion by virtue of the combustion of less fuel. Further, as a greater proportion of the fuel used during operation of the internal combustion engine is completely burned, the amount of pollutants associated with the emissions fuel may be reduced.
Although a number of prior attempts have been made to obtain a more complete combustion of fuel, those attempts have suffered from a number of possible drawbacks. For example, some prior attempts have required relatively expensive control systems, rendering such systems economically unattractive for certain applications. Other attempts have been found less reliable, rendering them unsuitable for long-term use and/or some applications.
Yet another possible drawback with some prior systems relates to an inability of the systems to tailor operation of the internal combustion engine to particular operating circumstances. For example, it may be desirable under some operating circumstances for an internal combustion engine to achieve maximum efficiency at the expense of responsiveness to changes in load. Such operational circumstances may occur, for example, when the internal combustion engine is being used at a relatively steady engine speed and/or a relatively constant load, such as, for example, the operational circumstances experienced by a lawn mower, or the operational circumstances experienced by a car, boat, or airplane when cruising at a relatively constant speed and/or altitude. On the other hand, some operating circumstances may result in a desire for increased responsiveness to changes in load at the expense of maximum efficiency. Such operational circumstances may occur, for example, when the internal combustion engine is being used in a car being driven in a city's stop-and-go traffic, or in an airplane during take-off or landing operations. Thus, it may be desirable to control the operation of an internal combustion engine in an efficient manner that permits the operation to be changed based on the operating circumstances, while minimizing undesirable exhaust emissions.